Radioactive iodine use in thyroid cancer on the rise despite its risks

Although substantial uncertainty persists regarding how to use radioactive iodine for thyroid cancer, the proportion of patients receiving this treatment is increasing, a recent study has determined.

Radioactive iodine is often administered after total thyroidectomy, as studies have shown that the treatment improves survival and reduces tumor recurrence in persons with iodine-avid, advanced-stage, well-differentiated thyroid cancer. However, for patients with very low-risk disease—who typically have an excellent prognosis—treatment with radioactive iodine is of uncertain benefit, explained Megan R. Haymart, MD, of the University of Michigan in Ann Arbor, and colleagues in JAMA (2011;306[7]:721-728).

Radioactive iodine use has transient adverse effects on quality of life and carries long-term health risks, such as a greater chance for second primary malignancies even in the lowest-risk patients (particularly leukemia, the risk of which increases 2.5-fold); other adverse systemic effects; and damage to the salivary glands, nasolacrimal ducts, and other local tissue. Radioactive iodine treatment also poses public health risks if the appropriate precautions are not taken at the time of administration.

“Because of limited clinical evidence, clinical guidelines have left radioactive iodine use to physician discretion in many cases,” wrote Haymart and team.

Nevertheless, when Haymart and colleagues analyzed radioactive iodine use in 189,219 persons with well-differentiated thyroid cancer treated at 981 US hospitals between 1990 and 2008, they found a significant increase in the proportion of patients receiving radioactive iodine across all tumor sizes: 1,373 of 3,397 patients (40.4%) underwent the treatment in 1990, compared with 11,539 of 20,620 (56%) in 2008. For tumors of 1.1 to 2.0 cm, 2.1 to 4.0 cm, and larger than 4.0 cm, there was a 55% to 67% increase in the percentage of patients treated in 2008 compared with those treated in 1990. “The proportion of tumors sized 1.0 cm or smaller treated with radioactive iodine was lower but has also increased steadily over time,” noted the investigators, who also found evidence that radioactive iodine may be underused in some high-risk patients. A statistically significant difference in radioactive iodine use existed between American Joint Committee on Cancer stages I and IV, but not for stage II or stage II vs stage IV.

Younger age and absence of comorbidity were associated with a small but significantly greater likelihood of receiving radioactive iodine after total thyroidectomy; females, African Americans, and the uninsured were less likely to undergo this form of adjuvant therapy. Radioactive iodine also was more likely to be used as the volume of thyroid cancer cases treated at a hospital increased.

“Wide variation in radioactive iodine use existed, and only 21.1% of this variation was accounted for by patient and tumor characteristics,” summarized Haymart and associates. “Hospital type and case volume accounted for 17.1% of the variation. After adjusting for available patient, tumor, and hospital characteristics, 29.1% of the variance was attributable to unexplained hospital characteristics.”

The authors found it “concerning” that disease severity appears to have a small influence on radioactive iodine use after thyroid surgery, adding, “In the interest of curving the increasing health care costs and preventing both overtreatment and undertreatment of disease, indications for radioactive iodine should be clearly defined and disease severity should become the primary driver of radioactive iodine use.”